Virologists Track New Influenza Threat

December 22, 1997

MADISON, Wisc. - University of Wisconsin-Madison influenza experts will conduct a detailed surveillance next month of the dangerous strain of influenza that has infected eight people and killed three in Hong Kong.

Yoshihiro Kawaoka, a virology professor in the School of Veterinary Medicine, will travel to Hong Kong in early January to identify the source of the virus, a type found commonly in birds. Finding the virus in animals is important in determining how the virus is being spread. If the spread is person-to-person, rather than extremely rare avian-to-person cases, it poses a more serious public health threat.

Kawaoka and UW-Madison post-doctoral fellow Peng Gao will team with Dr. Robert Webster of St. Jude's Childrens Research Hospital in Memphis for the month-long study, sponsored by the National Institutes of Health.

This strain of influenza, called H5 influenza, is found in birds worldwide and, in this case, is believed to have originated in chickens. A Hong Kong child who died of H5 influenza in May is the first documented case of a human contracting this type of flu. Since then, seven others have been diagnosed with this potentially lethal strain.

"There's no way of knowing at this point whether this virus will take off or die off in people," Kawaoka said, "but the surveillance in poultry will tell us what's out there. We have to work discreetly because at this point there is no need to make people panic."

Flu viruses commonly have changes in their surface proteins, called "drift," which makes flu viruses slightly different each year and requires new vaccinations. Of greater concern to virologists is a "shift," which occurs when a radically different strain enters people. A shift is believed to occur when genes from two different strains mix together.

Kawaoka said the team will test birds from chicken farms and on the market in Hong Kong. As a precaution, the scientists will take an antiviral drug called rimantadine, which blocks infection from the virus. Kawaoka said identifying the virus in birds and comparing it with the human cases will help determine whether any genetic variation exists between the two.

Kawaoka said these influenza cases surprised virologists. In 1983, a massive epidemic of H5 influenza decimated poultry and cost the U.S. Department of Agriculture $61 million to eradicate the virus. But extensive surveillance at the time found no reported cases in humans, leading scientists to believe the H5 virus was not readily transmitted to people.

Virologist Virginia Hinshaw, dean of the Graduate School and a UW-Madison influenza expert, said there are 15 different types of influenza distinguished by variations in their surface proteins. People and other mammals commonly get H1, H2 and H3 influenza and have antibodies that can fight off infection for those types.

The H5 virus is frightening because people have no antibody protection against this type. Any time a new influenza type is introduced in people, it raises the possibility of a larger epidemic. On top of that, Hinshaw said this H5 strain is lethal in birds, and we don't know of its potentially lethal effects in people.

The fact that the virus emerged in a major international trade center such as Hong Kong raises fears about rapid transmission, she said.

Scientists also need to learn whether this "all-bird" influenza type is acquiring any genes from influenza viruses common in people. That type of genetic variation could also make widespread transmission more likely, she said.

"This could very well die out like the swine flu did in 1976, but I wouldn't bet on it," Hinshaw said. "We certainly hope that it can't be easily transmitted."

Major shifts in influenza have caused global flu epidemics in the past. The 1918 flu epidemic, for example, killed 20 million people, and the Asian flu of 1957-58 and the Hong Kong flu of 1968-69 claimed thousands of lives.

University of Wisconsin-Madison

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